The present invention relates generally to crosslinkable waterborne polymer compositions, especially emulsions or dispersions. In particular, the present crosslinkable waterborne polymer compositions are useful as coatings or binders in one-pack storage-stable coating compositions which have low moisture permeability.
It is well known that the durability and aesthetic value of a variety of substrates can be maintained or enhanced by application of a polymeric coating to the surface of such substrates, and that crosslinking after application improves coating performance (for example, by improving film hardness and strength, as well as chemical resistance properties). These improvements are particularly beneficial to substrates that require protection from environmental stresses, or substrates to which abrasives or organic solvents (cleaners) are frequently applied.
Where polymer particle dispersions contain amine nitrogen reactive carbonyl functional groups, maintaining dispersion stability in the presence of polyfunctional amines is difficult. One method of obtaining a stable polymer particle dispersion in an aqueous carrier is to incorporate carboxy acid functional groups into the polymer backbone. It is thought that, in an aqueous carrier at a pH equal to or greater than the pKa of the acid group, some of the carboxy acid groups located on the surface of the polymer particles ionize and form a dispersion-stabilizing electric double layer around the polymer particle. Sufficient carboxy acid groups must be present to block effectively the reaction between the amine nitrogen groups of the crosslinking agent and the carbonyl groups present on the dispersed polymer particles. Examples of such compositions are disclosed in EP 555 774 A1 (Kriessmann et al.) and WO 93/16133 (Esser). The main drawback to this method is that, although the carboxy acid groups on the polymer backbone stabilize the dispersion, these groups also increase moisture permeability of the resultant coating. That is, in the resulting polymeric coating, the presence of the carboxy acid groups increases the amount of water which is able to pass through the coating or which is absorbed by the coating itself, thus allowing more water to attack the substrate.
An alternate method of stabilizing a polymer particle dispersion is to incorporate certain hydrophilic compounds (such as amine-functional polyalkleneoxide compounds) into the dispersion. Examples of such compositions are disclosed in WO 95/09209 (Serelis et al.), which teaches that use of a polyoxyalkylene amine crosslinker increases storage-stability of the compositions. These compositions, however, have the same drawback as the previously described compositions, since the presence of such polyoxyalkylene amines is also known to increase the moisture permeability of such coatings.
The problem of storage-stability is addressed in the above-mentioned references, but at the expense of coating performancexe2x80x94through either the incorporation of high amounts of carboxy acid in the polymer backbone, or the use of hydrophilic, dispersion stabilizing crosslinkers such as polyoxyalkyldiamines. What is desired, then, is a one-pack storage-stable composition where coating performance (i.e., water resistance) is not sacrificed.
The coating compositions of the present invention comprise: (a) a polymeric component comprising an aqueous dispersion of latex polymer particles neutralized to a pH of not less than 6, the polymer having a Hansch value of 1.5 or greater, an acid number of 0-25, at least 5 percent by weight (xe2x80x9cwt %xe2x80x9d) of a carbonyl functional group capable of reacting with a nitrogen moiety, and at least 1 wt % of a non-acidic functional group having hydrogen-bondable moieties; and (b) a crosslinking agent comprising a nitrogen-containing compound having at least two nitrogen functional groups capable of reacting with a carbonyl functional moiety, wherein the mole equivalents ratio of such crosslinking agent to reactive carbonyl moieties is at least 0.25:1.
As used in this specification, the following terms have the following definitions, unless the context clearly indicates otherwise. xe2x80x9cCrosslinkablexe2x80x9d and xe2x80x9ccrosslinkingxe2x80x9d refer to the formation of new chemical bonds between existing polymer chains, and xe2x80x9ccuringxe2x80x9d refers to the crosslinking polymers after application to the substrate. xe2x80x9cStorage-stablexe2x80x9d refers to a coating composition wherein the reactive components do not substantially crosslink within the storage container itself, even upon prolonged storage. xe2x80x9cPot lifexe2x80x9d or xe2x80x9cshelf lifexe2x80x9d refers to the period of time a composition is storage-stable. xe2x80x9cTwo-packxe2x80x9d or xe2x80x9ctwo-componentxe2x80x9d refers to coating compositions (or systems) wherein the components are stored separately, then are mixed together just before use; on the other hand, xe2x80x9cone-packxe2x80x9d or xe2x80x9cone-componentxe2x80x9d refers to coating compositions wherein the components are stored in one container. Ranges specified are to be read as inclusive, unless specifically identified otherwise.
The multi-component one-pack storage-stable coating compositions of the present invention will include at least 5 wt % solids of the carbonyl functional group containing polymeric component, based on the total weight of the final composition. It is preferred that the compositions of the present invention will preferably include 5-70 wt % solids of the carbonyl functional group containing polymeric component, and most preferably 10-50 wt %.
The polymeric component of the present invention may be prepared by emulsion polymerization or (aqueous) dispersion polymerization techniques known to those skilled in the art. Ethylenically unsaturated monomers may be used to prepare the emulsion or dispersion polymers that constitute the polymeric component of this invention. Examples of suitable monomers include ethylenically unsaturated monomer, such as, for example, acrylic ester monomers including methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, lauryl (meth)acrylate, isobornyl (meth)acrylate, isodecyl (meth)crylate, oleyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, hydroxyethyl (meth)acrylate, and hydroxypropyl (meth)acrylate; acrylamide or substituted acrylamides; styrene or substituted styrenes; butadiene; ethylene; vinyl acetate; vinyl ester of xe2x80x9cVersaticxe2x80x9d acid (a tertiary monocarboxylic acid having C9, C10 and C11 chain length, the vinyl ester is also known as xe2x80x9cvinyl versatatexe2x80x9d), or other vinyl esters; vinyl monomers, such as, for example, vinyl chloride, vinylidene chloride, vinyl pyridine, N-vinyl pyrrolidone; non-reactive amino monomers, such as, for example, N,Nxe2x80x2-dimethylamino (meth)acrylate, chloroprene, and acrylonitrile or methacrylonitrile. In addition, polyfunctional ethylenically unsaturated monomers may be incorporated, including allyl-, vinyl-, and crotyl- esters of acrylic, methacrylic, maleic, and fumaric acids, di- and tri-(meth)acrylate derivatives, divinylbenzene, diallylphthalate, triallylcyanurate, and polyvinyl ethers of glycols and glycerols. Suitable copolymerizable ethylenically-unsaturated acid monomers include, but are not limited to, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, monomethyl itaconate, monomethyl fumarate, monobutyl fumarate, maleic anhydride, 2-acrylamido-2-methyl-1-propanesulfonic acid, sodium vinyl sulfonate, and phosphoethyl methacrylate.
The polymeric component will have an Hansch value of 1.5 or greater, and an acid number of 0-25. The acid number of the polymer is preferably 1-20, and most preferably 5-15. The polymeric component will additionally contain at least 5 wt % (based on the weight of the monomer containing that group) of a carbonyl functional group capable of reacting with an amine nitrogen moiety, preferably at least 8 wt %, and most preferably at least 12 wt %; and at least 1 wt % (based on the weight of the monomer containing that group) of a non-acidic functional group having hydrogen-bondable moieties, preferably at least 3 wt %, and most preferably at least 5 wt %.
The hydrogen-bondable moieties of the polymeric component may include, but are not limited to, hydroxy, amido, alkylether, nitrilo, tertiary amino, or mercapto. Examples of such functional components include monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, acrylonitrile, acrylamide, methacrylamide, N-(hydroxyethyl)(meth)acrylamide, N,N-bis(hydroxyetthyl)-(meth)acrylamide, dimethylaminoethyl methacrylate, and chain transfer agents or initiators which contain hydrogen-bondable moieties, such as hydroxyethyl mercaptan, 2,2xe2x80x2-azobisisobutyronitrile, 2-(carbamoylazo)isobutyronitrile, or 2,2xe2x80x2-azobis[2-methyl-N-(2-hydroxyethyl) propionamide].
The amine-reactive, carbonyl-functional group of the polymeric component may include, but is not limited to, ketone- or aldehyde-functional ethylenically unsaturated monomers such as diacetone acrylamide, (meth)acryloxyalkyl benzophenone, (meth)acrolein, crotonaldehyde, 2-butanone(meth)acrylate, as well as active methylene compounds such as the esters and amides of acetoacetic acid. Preferred are the esters of acetoacetic acid. When monomer(s) that do not bear active methylene groups are used exclusively in the formation of the polymer or when additional acetoacetate groups are desired, acetoacetate groups may be introduced by the use of acetoacetate-functional chain transfer agents, such as those disclosed in U.S. Pat. No. 4,960,924 or by post-reaction of a copolymerized monomer. Cyanoacetates and cyanoacetamides may be prepared by methods known in the art as disclosed, for example, in U.S. Pat. Nos. 3,554,987; 3,658,878; and 5,021,511. U.S. Pat. Nos. 4,960,924; 3,554,987; 3,658,878; and 5,021,511 are hereby incorporated by reference herein.
In preparing the polymeric component, any chain-transfer agent, or mixtures thereof, may be used to control molecular weight. Suitable chain transfer agents include, for example, C1 to C12 alkyl or functional alkyl mercaptans, alkyl or functional alkyl mercaptoalkanoates, or halogenated hydrocarbons, and may be employed in the polymer at levels of 0.1-10 wt %, based on the weight of the polymer.
The ethylenically unsaturated monomers are typically polymerized in the presence of water-soluble or oil-soluble initiators (i.e., persulfates, peroxides, hydroperoxides, percarbonates, peracetates, perbenzoates, azo-functional compounds and other free-radical generating species).
Chelating agents may be used in emulsion or dispersion polymerization to provide stability. Such agents include those having multi-functional polar groups, and are capable of complexing with metal ions. Typical chelating agents useful in the present invention include but are not limited to: phosphoric acid, phosphates and polyphosphates; n-phosphonoalkyl-n-carboxylic acids; gem-diphosphono-alkanes and gem-diphosphonohydroxyalkanes; compounds containing one or more aminedi(methylenephosphonic acid) moieties, such as aminotris(methylene-phosphonic acid), ethylenediaminetetrakis(methylenephosphonic acid), and diethylenetriamine-N,N,Nxe2x80x2,Nxe2x80x3,Nxe2x80x3-penta(methyleenephosphonic acid); compounds containing one or more aminedi(methylenecarboxylic acid) moieties, such as N-(2-hydroxyethyl)ethylenediaminetriacetic acid (xe2x80x9cHEDTAxe2x80x9d), ethylenediaminetetraacetic acid (xe2x80x9cEDTAxe2x80x9d), and nitrilotris(methylenecarboxylic acid); as well as their alkali metal and ammonium salts. Such agents will be used in the present invention in amounts of 0-5 wt % based on the total weight of polymer.
Surfactants are commonly used in emulsion or dispersion polymerization to provide stability, as well as to control particle size. Conventional surfactants include anionic or nonionic emulsifiers or their combination. Typical anionic emulsifiers include but are not limited to: alkali or ammonium alkyl sulfates, alkyl sulfonates, salts of fatty acids, esters of sulfosuccinic acid salts, alkyl diphenylether disulfonates, and salts or free acids of complex organic phosphate esters. Typical nonionic emulsifiers include but are not limited to: polyethers, e.g. ethylene oxide and propylene oxide condensates which include straight and branched chain alkyl and alkylaryl polyethylene glycol and polypropylene glycol ethers and thioethers, alkyl phenoxypoly(ethyleneoxy) ethanols having alkyl groups containing from about 7 to about 18 carbon atoms and having from about 4 to about 100 ethyleneoxy units, and polyoxy-alkylene derivatives of hexitol, including sorbitans, sorbides, mannitans, and mannides. Surfactants may be employed in the compositions of the present invention at levels of 0.1-3 wt % or greater, based on the total weight of the final composition.
Any nitrogen-containing compound having at least two carbonyl group reactive amine nitrogens can be employed as the crosslinking agent in the present invention. Such compounds can be aliphatic or aromatic, polymeric or non-polymeric, and can be used alone or in combination. Examples of suitable compounds include: ethylenediamine, propylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, piperazine, aminoethylpiperazine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, cyclohexyldiamine, isopheronediamine, triaminoethylamine, diaminoethanolamine, phenylenediamine, and biphenyldiamine, hydrazine, alkyl dihydrazines, alkylene dioxime ethers, and water soluble dihydrazides of dicarboxylic acids (for example, dihydrizides of malonic, succinic, and adipic acids). Such crosslinking agent is used in an amount sufficient to react with at least 0.25 carbonyl functional group equivalents present in the polymeric component, preferably in an amount sufficient to react with at least 0.5 carbonyl functional group equivalents, and most preferably, at least 1 carbonyl functional group equivalents. That is, the mole ratio of such crosslinking agent to reactive carbonyl moieties is at least 0.25:1, preferably 0.5:1, and most preferably 1:1.
Other optional components that can be included in this invention include co-solvents, pigments, fillers, dispersants, wetting agents, anti-foam agents, UV absorbers, antioxidants, biocides, and stabilizers.
The multi-component one-pack storage-stable coating compositions of the present invention are generally prepared by blending the polymeric component and the crosslinking agent with agitation or stirring, then adding the optional components (as desired) in any order of addition which does not cause an incompatibility between components. Components which do not dissolve in the aqueous carrier (such as pigments and fillers) can be dispersed in the aqueous polymeric component or an aqueous carrier or cosolvent using a high shear mixer such as sand mill or Cowls mixers. The pH of the coating composition can be adjusted by adding an acid or a base, with agitation. Examples of base include, but are not limited to ammonia, diethylamine, triethylamine, dimethylethanolamine, triethanolamine, sodium hydroxide, potassium hydroxide, and sodium acetate. Examples of acids include, but are not limited to acetic acid, formic acid, hydrochloric acid, nitric acid, and toluene sulfonic acid.
The coating compositions of the present invention can be used to provide coatings on suitable substrates such as wood and reconstituted wood products, concrete, asphalt, fiber cement, stone, marble, clay, plastics (for example, polystyrene, polyethylene, ABS, polyurethane, polyethylene terphthalate, polybutylene terphthalate, polypropylene, polyphenylene, polycarbonate, polyacrylate, PVC, Noryl(copyright), and polysulfone), paper, cardboard, and metal (ferrous as well as non-ferrous).
The coating compositions of the present invention can be applied to desired substrates using conventional application techniques such as conventional or airless spray, roll, brush, curtain, flood, and dip-coating methods. Once applied to the substrate, the coating compositions can be cured at ambient or elevated temperatures.
Besides coating applications, the compositions of the present invention can be used alone or in combination with other components to provide, for example, adhesives, sizing agents, composites, impregnants, castings, caulks, and non-woven binders.